1. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 1 William Forrest (U of Rochester) Kyoung Hee Kim, Dan Watson, Ben Sargent (U. of R.) and IRS_Disks Team Full Accretion Disk by Robert Hurt (Spitzer Science Center) Spitzer-IRS spectra of transitional disks in the Chamaeleon Cloud

2. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 2 Transitional disks, and why they are important  Transitional disks: protoplanetary disks with central clearings or radial gaps.  Clearings and gaps (and details of their structure) can be revealed by the wavelength dependence of infrared excess.  In ~1-2 Myr-old objects, such clearings are most easily explained by giant-planetary formation (e.g. Forrest et al 2004, d’Alessio et al. 2005, Calvet et al. 2005).

3. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 3 IRS/Spitzer Spitzer Space Telescope  Launched on 25 Aug. 2003  Three scientific instruments : Infrared Spectrograph (IRS) (Houck et al., 2004) Infrared Array Camera (IRAC) Multiband Imaging Photometer (MIPS) IRS (Infrared Spectrograph) ▫ Composed of four modules - λ/Δλ ~ 64-128 (SL, LL), λ/Δλ ~ 600 (SH, LH) ▫ Sensitive in 5-40 μm wavelength range Clockwise from the top: IRS, IRAC, MIPS ▫ Suitable for looking at faint IR sources including protostars and protoplanetary disks

4. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 4  88 YSOs in Chamaeleon I & II dark cloud observed during Campaign 20, 21, and 22.  IRS staring mode, SL-LL, SL-SH-LH  S13 pipeline, BCD Data (flatfielded, stray-light corrected, dark current subtracted)  Bad pixel fixing  Extraction of spectra using SMART (Sky subtraction, RSRF calibration) (Higdon et al., 2004)  7 Transitional Disks candidates Observation & Data Reduction Sz 18 CHXR 30 UX Cha Sz 27 Ced 110 IRS2 CS Cha CHX 22

5. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 5 IRS spectra of Transitional Disks with central clearings in Cha I  Extinction corrected with Av/τ(9.7μm) = 18.5 and the opacity from Draine(2003) for Rv=3.1  Kurucz photospheric models fit to J, H, K NIR photometry Cha Class II median spectrum (normalized at H band) IRS spectrum 10 μm silicate feature 20 μm silicate feature

6. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 6  photosphere subtracted from the IRS spectrum  best BB temperature chosen to fit the dust continuum  Dust opacity ~ equal at 13 and 30  m  T wall (wall temperature)  R hole (radius of hole) from the radiative equilibrium Assuming a black, insulating wall facing the star ( no free parameters!) (test against CoKu Tau/4, DM Tau ) Radius of central clearings Sz 18 CHX 22 CS Cha Ced110 IRS 2Sz27UX Cha CHXR 30 CoKu Tau/4 DM Tau R hole (AU)10.12523124191359.34.2

7. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 7 Check on Derived Hole Radius Sz 18 CHX 22 CS Cha Ced110 IRS 2Sz27UX Cha CHXR 30 CoKu Tau/4 DM Tau R hole (AU)102523124191359.34.2 Superheated Silicates 5.5>2410n.a.7.8n.a.2.1 Assumed 103.0 Real Model103  Toy model: Subtract optically thick “continuum” fit to 5-8  m From 10-20  m color temperature, calculate dust temperature Calculate radius to reach this temperature Dust is ‘superheated’, absorbs at short wavelengths better than it emits Scale using 10 AU for CoKu Tau/4

8. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 8 Upper mass limit of small dust gains in the hole Must be considerably less than the optically thin, upper layers of Classical (Class II) T Tauri stars.  Use same toy model: From 10-20  m color T, calculate average dust T, Observed flux is Size of region: maximum optical depth (10  m) = 0.1 FM TauIP TauGG Tau A GG Tau B FN Tau V 410 Anon 13 CY Tau M dust /M Moon 4 10 -3 2 10 -3 5 10 -3 0.3 10 -3 8 10 -3 0.1 10 -3 0.3 10 -3 R(AU)323.30.940.60.8  M dust (trans.)/M dust (opt. thick) ≤ 10 -5  Can be done by giant-planet formation in < 10 5 yr (Quillen et al. 2004, Varniere et al., 2006). Can’t be done by radiative means, in the age of the objects.

9. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 9 Transitional disks frequency  Transitional disks in the Taurus-Aurigae cloud 151 objects observed, 85 objects are classified as Class II YSOs, 3 transitional disks, two of which (CoKu Tau/4, DM Tau) have central clearings Frequency = 2/85 ~ 0.02  Transitional disks in the Chamaeleon cloud 88 objects observed, 65 objects are classified as Class II YSOs, 7 transitional disks with central clearings Frequency = 7/65 ~ 0.11  More evolved YSOs in Cha I cloud than Tau-Aur cloud region?

10. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 10 Transitional disks trend : T eff vs. R hole

11. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 11 Conclusion & Future Work  Seven protoplanetary disks in Cha I with sharp-edged central clearings  Upper limit to mass of small dust grains in central clearing typically 10 -3 lunar mass.  Planetary formation in first ~1-3 Myr still best explanation for these structures.  Higher frequency of the transitional disks with central clearing in Chamaeleon cloud than in Taurus-Aurigae cloud  more advanced state of evolution for Cha I ?  Need to work on detail models to get more accurate R hole and the upper mass limits of small dust grains inside the central clearing region and to understand the central dust clearing mechanism in holes.  Need to search Cha I IRS spectra for transitional disks with radial gaps (like Taurus/Auriga’s GM Aur)  Similar survey of the Ophiuchus cloud on the way.

12. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 12 References (selected)  D’Alessio et al., 2005, ApJ, 621, 461  Forrest et al., 2004, ApJ, 154, 443  Calvet et al., 2005, ApJ, 630, L185

13. U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 13 IRS/Spitzer Spitzer Space Telescope  Launched on 25 Aug. 2003  Three scientific instruments : Infrared Spectrograph (IRS) (Houck et al., 2004) Infrared Array Camera (IRAC) Multiband Imaging Photometer (MIPS) IRS (Infrared Spectrograph) ▫ Composed of four modules - λ/Δλ ~ 64-128 (SL, LL), λ/Δλ ~ 600 (SH, LH) ▫ Sensitive in 5-40 μm wavelength range Clockwise from the top: IRS, IRAC, MIPS ▫ Suitable for looking at faint IR sources including protostars and protoplanetary disks